There is a technology in which a predefined identifier (mark) is provided on an industrial product and background information on the industrial product becomes traceable throughout procurement, processing, production, distribution, sales, disposal, and the like. Ignition plugs configured to ignite air-fuel mixtures in internal combustion engines are also required to have marks in order to increase the traceability. As a technology for providing a mark on an industrial product, Japanese Registered Utility Model No. 3078913 discloses a technology of printing a mark by radiating a laser beam onto the surface of a ceramic base.
In the related art, however, the mark is formed by radiating the laser beam onto the surface of the ceramic base that is a brittle material. Therefore, the mark may trigger breaking of the base, thereby causing a risk that the strength of the member having the mark may decrease.